They left the country in December, but Grannis has only now revealed the ordeal.

She wrote on her blog she decided to write about it now because otherwise "it will have all been for nothing — as if I'd been simply robbed of three months of my life".

Suspicious immigration officials were in the crowd during her concert last year at the city's popular Salihara venue.

Indonesian immigration officials told the ABC they approached the band onstage at about 2:00am, moments after the concert was finished.

"South Jakarta immigration office personnel had an operation for illegal aliens and they caught 14 foreigners in the Pasar Mingu area who at the time were doing musical activities," spokesman for the immigration department Heru Santosa Ananta Yudha said.

The band's promoters had not organised the right visas.

Indonesia has extremely strict rules about foreigners working in the country.